Crazy about one domestic (4)
I believe the answer is:
maid
'domestic' is the definition.
(I know that maid is a type of domestic)
'crazy about one' is the wordplay.
'crazy' becomes 'mad' (synonyms).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'mad' enclosing 'i' is 'MAID'.
(Other definitions for maid that I've seen before include "Female domestic servant" , "Young woman - servant" , "Serving girl" , "employee" , "Damsel" .)